Fluke DDS Function Generator 271, Руководство пользователя

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Triggered Burst and Gate
Triggered Burst
7
7-3
Trigger Source
With the edit cursor in the
SOURCE
field of the trigger edit menu, the DIGIT keys or
rotary control can be used to select
EXT
ernal,
MAN/REMOTE
, or
TGEN
(internal
trigger generator) as the trigger source.
With the source set to
EXT
ernal, the specified burst is triggered by the rising edge of a
trigger signal applied to the EXT TRIG input (see External trigger input above). With
the source set to
MAN/REMOTE
, a burst can be initiated by pressing the front panel
MAN/SYNC key or by the appropriate command via the RS232 or GPIB interfaces.
With the source set to
TGEN
, the burst is triggered internally as described above in the
Internal trigger generator section. The period of the internal generator is set in the
TGEN
field on the second line of the edit menu. With the cursor in the numeric field the
DIGIT keys will move the cursor within the field and the rotary control will change the
value in increments determined by the cursor position; with the cursor in the units field
the
DIGIT keys or rotary control will change the value in decade increments. Direct
keyboard entries (number plus units) will be accepted with the cursor in either field.
Beside the generator period value the equivalent frequency is shown; this is for
information only and is not an editable field.
Because the internal trigger generator can be used by the trigger, gate, FSK and AM
functions, and can be set from their respective edit menus, an information field is
displayed in brackets beside
TGEN
when this is selected as the source. This field will
show
[FREE]
when
TGEN
is not used elsewhere, or one of the four letters
G, F
,
A
or
T
to indicate that the generator is currently set as the source on the
GATE
,
FSK
,
AM
, or
TRIG
menus respectively, in addition to the menu currently displayed.
Burst Count
The number of complete cycles in each burst following the trigger is set with the edit
cursor in the
BURST COUNT
field. Entries can be made directly from the keyboard or
by rotary control; the burst range is 1 to 1023 with a resolution of 1 cycle or 0.5 to 511.5
with a resolution of 0.5 cycles. The first cycle starts, and the last cycle stops, at the phase
set in the
PHASE
field.
Start/Stop Phase
The start and stop phase of the triggered burst is set in the
PHASE
field. The field
actually contains the phase of the auxiliary output and it is from this output that control of
the start and stop point of the main generator is derived; the rising edge of the
AUX OUT
signal, which can be phase shifted with respect to the MAIN OUT , determines the start
and stop point of the main waveform burst. Consequently, the conditions under which the
auxiliary output phase shift is constrained, and which are fully explained in that section,
all apply to start/stop phase. For example, the start/stop phase of sine and triangle
waveforms cannot be adjusted for main output frequencies above 30 kHz unless the
AUX OUTPUT
field on the options menu is set to
LOW FREQ
uency generation mode
because only in this mode does the AUX OUT continue to be phase shifted with respect
to MAIN OUT .
Because the phase control signal is derived from the auxiliary output waveform further
considerations apply as the main generator frequency is increased. With
AUX OUTPUT=LOW FREQ
on the
Options
menu, phase shift control is still
available above 30 kHz but real hardware delays become increasingly significant such
that the start/stop phase increases for no change in phase setting; this shift is caused by
the delay between
AUX OUT and MAIN OUT becoming more significant and by the
delays in the burst count and phase control circuits themselves. These delays can be
equivalent to a phase shift of about +45 ° at 1MHz; however, by ‘backing off’ the
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